Hydraulic draft tube



Dec. 11, 1928.

L. F. MOODY HYDRAULIC DRAFT TUBE 2 Sheets-Sheet 1 Original Filo ad Nov.28. 1922 Z5 z? 7 Z-r- Z6 r? I mi? Elwvemtoz Zm zo 1010002,;

Patented Dec. 11, 1928.

PATENT OFFICE.

LEWIS FERRY IvIOODY, OF PHILADELPHIA, PENNSYLVANIA.

HYDRAULIC DRAFT TUBE.

Original application filed November 28, 1922, Serial No. 603,769.Divided and this application filed March 26, 1926, Serial No. 97,534.Renewed May 14, 1928.

This invention relates to hydraulic turbines and in particular to animproved means for receiving water from the turbine runner anddelivering it to the tail race. More particularly my invention relatesto means or this character wherein the water is turned or spread outfrom a direction along the axis of the runner into diverging; radialdirections and is subsequently turned into a single direction fordischarge into the tail race. This application is a division of mycopending application, Serial No. 603,769, filed November 28. 1922.

In many modern hydraulic power plants the turbinesare placed in a rowwith vertical shafts, the water entering the turbines on one side of therow from the penstoclzs or forebay and discharging at the other sideinto the tail race. Tlhe water leaves the runners in a downwarddirection at high velocity and some means should be provided which willre duce this velocity so as to correspondingly reduce the back pressureon the turbine runners and which will likewise turn the flow into ahorizontal downstream direction. means should be constructed so toperform these functions without appreciable losses of energy and shoulditself occupy a minimum space. The last condition is particularlydesirable in order that the turbines themselves may be closely spacedand the power house dimensions made as small as possible.

F or the purpose of reducing the velocity,

draft tubes have been used which direct the flow iii in the runnerradially out ard on spreading lines and discharge it horizontally inevery direction. The flow may then be received by a collector whichturns it into a.

common downstream direction. Certain portions of theilow must be turnedthrough substantially 180 while other portions. which leave the tubein adirection more nearly approaching the downstream do not have to beturned through so great an angle.

If an unlimited space were available the initial velocity with which thewater enters the draft tube could be reducedand its kinetic energyturned into effective head for the turbine by the use of the spreadingaction alone, that is, the water could be discharged outwardly in alldirections at such a low velocity that but little kinetic energy wouldremain in it. The problem of collecting the flow and discharging itdownstream would be solved by the use of any suitable collector-Thiswhich would not cause an appreciable loss of head.

VVit-h the available space limited, however. it is desirable to providea draft tube of such dimensions that the water discharged into thecollector will retain a portion of its kinetic energy and that thecollector be so de signed as to reduce farther the velocity of the waterand to regain this energy. The water leaving the draft tube in anupstream direction may be conveniently collected from the tube by one ormore spi al passages extending; circumterentially around the cylindricaloutlet of the tube and discharging tangentially downstreamtoward thetailrace. These spiral passages should be enlarged at a rate than isnecessary to accommodate the cinnulative flow so that the velocity ofthe liow therethrough will be gradually reduced. One of the objects ofthe present invention to provide an improved collector of this characterwhich is designed to receive a flow of considerable velocity from thedraft tube and is adapted gradually anduniformly to re .uce the velocityof thisi'low and so regain kinetic energy. V Another object of myinvention is to pro vi e in addition to the spiral collector passagesabove described an effective means for de elerating that portion of theflow which oes not en er the spiral passages.

l lurnerons other objects and advantages will appear from the followingdescription ha? n in connection wi h the accompanying 0* rings whichillustrate certain of the pre- -c red embodiments of my invention andwherein Fig. 1 is a sectional view on line l1 of is a horizontalsectional view on the line f2-2 of Fig. l,

l e line 3-3 of Fig. 2, Fig. at shows a vertical section taken on theline il of Fig. 2 looking in'the direction of the arrows,

Fig. 5 shows in vertical section on the line 5 5 of Fig. 6, amodification, v N Fig. 6 is a horizontal section on the line 6-6 of Fig.5,

Fig. 7 is a vertical section on the line 7- -7 of Fig. 6, and p Fig. 8isa vertical sectionon the line 88 of: Fig-6 taken inthe directionof thearrows.

Referring to the figures, reference char- 3 shows a vertical sectionalView on acter 20 indicates generally the primary draft tube and 21 thecollector. The primary draft tube as shown is formed of an outer wall 22having a slightly tapered or conical upper portion 23 and graduallycurved outward to a horizontal direction at its lower end, the lower endof the draft tube having a barrel portion 28 depending into thecollector. The outer surface of the main body portion of the barrel iscylindrical. Projecting upwardly from the floor 25 of the collectorpassage into the flaring end of the wall 522 and concentric therewith isa cone 26 whose concave surface is formed in relation tothe outline ofthe fiaredend of the wall 22. The outer wall 22 and cone 26together termthe primary draft tube which serves to direct the flow downward from theturbine runner and outwardly into a horizontal plane. The crosssectional area of this tube as shown increases gradually so as to .givea gradual deceleration to the maridian components of the flow, and atthe same time the tube is adapted to handle eiiicientl y flow containingwhirling components about the turbine axis.

, In the form shown in Figs. 1 to 4 I provide a single curved collectorchannel which starts at a lateral point l at the mouth of the drafttube, is curved around the axis of the tube through an angle ofapproximately 180 and terminates in a straight passage 4:? having adirection downstream and substantially tangential to the draft tube. Theinner and outer walls of this passage are vertical and its upper andlowerwalls horizontal except that the upper wall 50 of the outer passageis in' clined upward at an angle preferably not to exceed about Thepassage 49 for discharing the direct flow is substantially rectangularin crosssection and is formed by the floor 25, top wall 50 which isinclined upwardly at an angle not to exceed about side wall 51 and wall52, the last being formed by a partition 53 which separates the passagefor the direct flow from the'end of the curved passage. The top wallthereby forms an extended roof with which the primary draft tube mergesto form the direct discharge passage whiehis also substantially tangentto the primary tube or passage at a point lateral of or offset from theaxis of the primary tube. it is also seen that only the two passages 47and 4-9 are providedi these having upper walls or roofs at differentelevations.

The form of my invention shown in Figs. 5 to 8 is similar to that shownin Figs. 1 to 4- except in the former the curved collector passage doesnot terminate in astraight section but continues to curve so that thetotal curve exceeds 180 and also continues to flare horizontally throughits entire course. This passage is quite narrow but considerably higherthan those shown in previous figures. T he partition of Figs. 1 and 2 isomitted,

there being merely a strut 56 betweenithe upwardly extending top wallofthe passage for the direct flow and the floor 25. The cone shown inthis form of my invention extends upwardly through the entire draft tubeto the runner and the runner shown is of the propeller type. If desiredthe form shown in these figures may have an over-hanging passagecollector.

lVhile I have shown a primary draft tube which constructed toprogressively increase in area, in certain cases it may be necessary toemploy one whose principal function is to turn the water outwardly inall directions without being able to produce any substantial decrease invelocity. such tubes it would be necessary to employ a collector whichwill reduce the velocity of the flow from an amount which is onlyslightly less than its velocity at the runner.

Moreover even with these turbines wherein the discharge velocity fromthe spreading co duit is sufliciently small to be so thrown away whenthe turbine is operating at its normal capacity, it must be consideredthat under the usual conditions turbines are frequently called upon tooperate at capacities considerably above normal and when so operatingthe discharge velocity from the spreading conduit rapidly increases andmay represent a very material amount of velocity head in comparison withthe available head on the plant. A failure to'provide for ellicientdeceleration of this velocity of discharge from the spreading orprin'iary draft tube may therefore materially restrict the fullloadcapacity of the turbine even in cases where the primary or spreadingconduit is sufiicient in itself to take care of the ordinary and normalload conditions with high e'tliciency. The proper formation of thecollector passages therefore may have a vital effect upon the fullpowercapacity of the turbine.

it should also be considered that by proefiicient collector passages thesize of "y portion of the draft tube may be without serious loss ofdraft tube my but with a material reduction in the over-all dimensionsof the entire draft tube, and consequently of the power-house andsub-structure.

lt hile T have shown my invention as applied to turbines having verticalaxes it is obvious that with slight modification of structure myinvention is likewise applicable. to turbines having horizontal shaftsJI have also shown a draft tube and collector which receive waterin anaxial directionand discharge it in radial or tangential direction, thatis, along a plane at substantially right angles to the axis of thedrafttube. It is of course apparent that the angle between the axis andthe discharge direction need not be exactly a right angle asconditionsof practice With the use of might makeit desirable to increase ordecrease this angle somewhat.

'Vhile in the foregoing description I have distinguished between theprimary draft tube and the collector, it will be recognized that inother forms, of my invention the primary draft tube and collectorfunction may be so merged that no one portion of the structure may betermed a primary draft tube and the remainder a collector. Such. casesmay nevertheless fall clearly within the scope of the present inventionas set forth in the appended claiins.

By radially spreading draft tube as employed in the claims I. mean atube which discharges the flow radially outward in all or let of saidtube being cut away to form a spiral collector passage, and saidspreading wall being continued in one direction to form an inclined wallof a second passage which receives the downstream flow directly fromsaid tube, and a partition for separating said spiral and downstreampassages.

2. A turbine having a draft tube formed of an outer circular spreadingwall and a central cone projecting into the space surrounded by saidwall, said spreading wall at the outlet of said tube being cut away toform a spiral collector passage, and said spreading wall being continuedin one direction to form one wall of a second passage which receives thedownstream flow directly from said tube, and a partition disposedbetween said spiral and downstream passages, one of said passages beinglocated tangential to said tube and adapted to receive therefrom a flowhaving tangential. component of velocity.

3. A turbine having a draft tube formed of an outer circular spreadingwall and a central cone projecting into the space surrounded by saidwall, said spreading wall at the outlet of said tube being cut away toform a spiral collector passage of rectangular cross section, and saidspreading wall being continued in one direction to form one wall of asecond passage which receives the down-. stream flow directly from thetube, and means forming a wall for both of said passages.

4:- A turbine having a draft tube formed of an outer circular spreadingwall and a central cone extending through the entire space surrounded bysaid wall, said spreading wall at the outlet of said tube being cut awayto form a spiral collector passage of a gradually increasing crosssection and said wall in one direction being continued along a surfacewhich is slightly inclined from thenormal to the axis of said tube toform one wall of a second passage which receives the downstream flowdirectly from said tube, and means forming anotherwall of one of saidpassages.

5. In a turbine a radiallyspreading draft tube and a collector adaptedto receive the flow from said tube and being offset with respect to saidtube, said collector being of progressively increasing area, andadaptedto produce a gradual deceleration of flow therethroughand beingprovided with a partition to prevent the mingling therein of streams ofdifferent velocities.

6. A turbine formed with a draft tube anda collecting chamber, theoutlet of said draft tube being partly formed-by a projection ex tendingfrom the wall of said collection cha1nher, said projection'beingextended in a downstream direction and offset relative'to said tube, anda pier between the extension and opposite wall for supporting saidprojection.

7. .A draft tube formed by two concentric surfaces of revolution turningfrom a substantially axial "direction to a radially outward direction,said surfaces terminating at a greater distance from the axis in oneportion of the circumference than the remaining portion and a collectorsurroundingsaid tube and extending in a downstream direction therefrom,said collector having a portion of its floor and roof diverging in thedirection of flowand the outer one of said 1 concentric surfacesterminating within said collector passage ata point below the adja- Icent roof portion. of the collector passage.

8. The combination with a draft tube, of a sage for receiving thedirectdownstream flow from the draft tube. I 9. The combination with adraft tube, of a collector having a passage provided with a spiral Wallstarting at a lateral point of the draft tube, and means forming asecond pas sage for receiving the direct downstream flow from the drafttube, said direct downstream passage extending inwardly from saidlateral point to a point intermediate said lateral point and the spiralwall.

10. The combination with a draft tube, of a collector having a passageprovided with a spiral wall extending in an upstream direction from alateral point of the draft tube and curving into. a downstreamdirection, and means forming a passage for directly discharging thedownstream flow from the draft tube, the depth of said spiral wall beinggreater than that of the direct discharge passage.

11. The combination with a draft tube, of a collector having a passageprovided with a spiral wall extending in an upstream direction from alateral point of the draftitube and curving into downst-reanr direction,and means forming a passage for directly C115;

charging the downstream flow from the draft tube, the depth of saidspiral wall being greater than that of the direct discharge passage, andsaid direct: discharge passage; having-a verticallyrinclinedsurface inthe down 12. The combinationwith adrafttube, of.

a collector having a passage provided with a spiral wall extendingin anupstream direction from apoint laterally otthe draft tube:

andrthen curving into a downstream direction, thereby permittingupstream flow from the draft I tube to be turned in .a a downstreamdirection, means torminga passage extending inadownstremn direction:for: receiving the direct downstream discharge i'rom the draft tube, andacone disposed in S2t1l1-'(l121ft.tllb.

for directing fluid flowto thedirectdischarge passage and to saidpassage having said spiral wall.

13.- The combination:with adratt tube having a flaring-inner wall and aprojecting-bar.-

rel portion, a collector passage surrounding said barrel, anouter'portion of the main body of said barrel beingcylindrical, andanother portion of the draft tubemerging with an extended root of saidcollector passagein a downstream direction, said passage which surroundssaidbarrel having a spiral 1 wall.

15. The combination with a drafttube, of a collector passage forreceiving the discharge from said tube, comprising means forming apassage substantially tangent to said draft tube and being-offset withrespect-to the central downstream H-XISOf the collector passage,

and'means forming a second passage surroundingone s1de ofthe draft tube,one of said passages having a roof disposed at'an elevation difl'ercntirom the roof of: ch-exotherpassage.

16. 'lhe-combi-nation with a a draft. tube, of a collec-torp assagetorreceiving tlie discharge troinsaiditube, comprising means forming apassage substantially tangent to 1 said draft;

tube at alateral pointthe-reol, means tor1ning a second passagesurrounding one s1de oitthe dratttub'e, one of said passages having aroof disposed at an elevation :difl'ferentii rom.

the root of the otherpassage, and apier disposed'at the juncture ofsa-idlroots forrsupporting the same from the floor of saidpassages. v

17. The COHlblntltlOIl*Wltllit draft tube, of a collector passageconstituting only two.

downstream passages,-one otiwhich has a roof.

disposedat an elevation different from the root oflthe other passage.

18. The combinationwitha dratt'tube, of

a collector passage having only apairot' downstream passages whosecombined Width is ofiset withrespect to the draft tube axis, and theroofs of" the respective passages being at different elevationsr 19. Aturbine having a draft tube formed.

of an outer circular spreading wall and a central cone pro ect1ng into:th eespace sur rounded by said a wall, said spreading wall:

at the. outletot said tube being cutaway to form a spiral collectorpassage, and said spreading wall being continued in 011G.Cli1'GC.- tionto form an inclined horizontally extending wall of-a second passagewhich receives the downstream flow directly from said tube.

and a partition spaced downstream from said cone 'l'o-r separating saidsplral and down stream passages.

20. In a turbine a radially spreadingclraitt' tube and a collectoradapted te receive the flow from said tube and being offset with re-vspect to said tube, said collector being of progressively increasingarea, and adapted to produce a gradual deceleration of flowthereth'rough and being provided with apartitio n to prevent themingling therein of streams of different velocities;

IiEl VIS FERRY MOODY.

